Ablation emitter assembly

ABSTRACT

An emitter assembly can include a proximal shaft, a distal shaft, a shunt that connects the proximal shaft to the distal shaft, and a tip that is connected to a distal end of the distal shaft. An inner conductor can extend through the proximal shaft, the shunt, and the distal shaft and into the tip to provide microwave energy to the tip. An outer conductor can extend into the shunt. The shunt can therefore form an electrical connection between the outer conductor and a proximal ring of electrically conductive material formed on an exterior surface of the distal shaft. Distal shaft can be made of a thermally conductive but electrically insulated material to facilitate transfer of heat from the distal shaft to the proximal shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

N/A

BACKGROUND

Microwave ablation (MWA) is a medical procedure where in vivo tissue isablated using high frequency electromagnetic field to treat a medicaldisorder. MWA is commonly performed to treat tumors in body organs.During MWA, a needle-like MWA probe is placed inside the tumor.Microwaves emitted from the probe heat surrounding tumor tissue,destroying the target tissues, such as soft tissue, cancerous tumor,nerve, or other target structure. Cancer cells, in particular, breakdown and die at elevated temperatures caused by MWA procedures. Some MWAprocedures create temperatures up to or exceeding 300 degrees Celsius.

For MWA to be successful, a sufficient amount of molecular agitationmust occur within the tissue. For example, the varying electromagneticfield generated by the waves emitted from the MWA probe causes watermolecules to rapidly vibrate as they attempt to align with the varyingfield. This molecular agitation creates frictional heat which is capableof rapidly increasing the temperature of the tissue in a similar manneras a microwave oven heats food.

It is desirable to heat the entire area of the tumor with a singletreatment. However, it is difficult to obtain even heat distributionusing current ablation techniques. When heated to above 60° C., tissuewill immediately coagulate.

BRIEF SUMMARY

The present invention extends to an emitter assembly that can be used toperform microwave ablation (MWA). The design of the emitter assembly canfacilitate transfer of microwave energy into a patient's tissue whilealso facilitating transfer of internal heat towards a proximal end ofthe emitter assembly thereby enabling operation of the emitter assemblyat higher power without sacrificing the accuracy of the ablationpattern.

In one embodiment, the present invention is implemented as an emitterassembly for performing an ablation that includes a proximal shaft, adistal shaft having an exterior surface, a tip that extends from adistal end of the distal shaft, an inner conductor that extends throughthe proximal shaft, an outer conductor, and a conductive trace formed onthe exterior surface of the distal shaft.

The distal shaft may be comprised primarily of ceramic including aluminabased ceramic or zirconia based ceramic. The tip may be the samecomponent as or a separate component from the distal shaft. The tip mayalso be comprised of an inner and an outer component. The conductivetrace may spiral around the exterior surface. The conductive trace maybe metallized onto the exterior surface of the distal shaft. Theconductive trace may extend in a proximal or a distal direction. Theconductive trace may also comprise multiple conductive traces thatextend in a proximal and a distal direction.

The distal shaft may include a distal ring and/or a proximal ring thatis formed on one or both of an interior surface or an exterior surfaceof the distal shaft. The tip may form an electrical connection betweenthe inner conductor and the distal ring. The conductive trace may beelectrically connected to the distal ring and/or the proximal ring.

The emitter assembly may include a shunt that connects the proximalshaft to the distal shaft. The shunt may form an electrical connectionwith the outer conductor. The proximal ring may be electricallyconnected to the shunt.

The emitter assembly may include an insulator positioned between theinner and outer conductors. The insulator may comprise PTFE or ceramic.The inner assembly may include an outer coating that covers at least aportion of an exterior surface of the distal shaft. The outer coatingmay cover one or more of the tip, the shunt, or the proximal shaft. Theouter coating may comprise one or more layers or may comprise glass,PTFE, or diamond-like carbon. The emitter assembly may comprise one ormore inner coatings applied on an inner surface of the distal shaft. Theone or more inner coatings may be applied over a portion of the proximaland/or distal rings that extends along an inner surface of the distalshaft.

In another embodiment, the present invention is implemented as anemitter assembly for performing an ablation that includes a distalshaft, a tip that extends from a distal end of the distal shaft, a tracethat extends along an exterior surface of the distal shaft, and an outercoating applied on the exterior surface overtop the trace. The distalshaft may be comprised of ceramic.

In another embodiment, the present invention is implemented as anemitter assembly for performing an ablation that includes a proximalshaft, a distal shaft, and a shunt for connecting the proximal shaft tothe distal shaft. The shunt comprises a conductive material fortransferring heat from the distal shaft to the proximal shaft.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates a microwave ablation device that can be used in MWAablation procedures;

FIG. 2A illustrates a front view of an example emitter assembly inaccordance with one or more embodiments of the invention;

FIG. 2B illustrates a cross-sectional view of the emitter assembly ofFIG. 2A;

FIG. 2C illustrates a detailed view of a distal portion of FIG. 2A;

FIG. 2D illustrates a detailed view of the shunt depicted in FIG. 2C;

FIG. 2E illustrates a detailed view of an alternate implementation ofthe shunt depicted in FIG. 2D;

FIG. 2F illustrates a detailed view of the tip depicted in FIG. 2C;

FIG. 2G illustrates a detailed view of an alternate implementation ofthe tip depicted in FIG. 2F;

FIG. 3 illustrates an exploded view of some of the components of theemitter assembly depicted in FIG. 2B;

FIG. 4A illustrates a cross-sectional view of a distal shaft after thedistal ring, the trace, and the proximal ring have been applied;

FIG. 4B illustrates a cross-sectional view of the distal shaft of FIG.4A after an outer coating has been applied;

FIG. 4C illustrates a cross-sectional view of the distal shaft of FIG.4B after a first inner coating has been applied;

FIG. 4D illustrates a cross-sectional view of the distal shaft of FIG.4C after a second inner coating has been applied;

FIG. 5A illustrates a front view of a distal shaft with variousdimensions labeled;

FIG. 5B illustrates a cross-sectional view of the distal shaft depictedin FIG. 5A with various dimensions labeled;

FIG. 6 illustrates a front view of an alternate embodiment of the distalshaft shown in FIG. 5A in which an end of the conductive trace isrounded;

FIG. 7 illustrates a front view of another alternate embodiment of thedistal shaft shown in FIG. 5A in which the conductive trace is connectedto the proximal ring;

FIG. 8 illustrates a front view of another alternate embodiment of thedistal shaft shown in FIG. 5A in which the pitch of the conductive traceis varied;

FIG. 9 illustrates a front view of another alternate embodiment of thedistal shaft shown in FIG. 5A in which the width of the conductive traceis varied;

FIG. 10 illustrates a front view of another alternate embodiment of thedistal shaft shown in FIG. 5A in which the distal shaft does not includea proximal ring;

FIG. 11 illustrates a front view of an alternate embodiment of thedistal shaft shown in FIG. 5A in which the distal shaft includes asecond conductive trace;

FIG. 12 illustrates a front view of an alternate embodiment of thedistal shaft shown in FIG. 5A in which the distal shaft does not includea distal ring;

FIG. 13 illustrates a front view of an alternate embodiment of thedistal shaft shown in FIG. 5A in which the distal shaft includes adistal ring that partially extends around the distal shaft;

FIG. 14 illustrates a partially transparent front view of an exampleemitter assembly configured in accordance with one or more embodimentsof the invention; and

FIGS. 15A-15C illustrate different views of a tip that can be used inplace of the distal shaft and tip shown in FIG. 2A.

DETAILED DESCRIPTION

FIG. 1 is intended to provide an overview of the general architecture ofa microwave ablation (MWA) device 100 that can be used in MWAprocedures. The MWA device 100 can include a body 101 and an emitterassembly 110 that is configured to attach to and extend from a distalend of body 101. Emitter assembly 110 can have various lengths asindicated by the break 115 in FIG. 1 and may typically be between 1 and12 inches. The gauge of emitter assembly 110 can range between 8 to 24,including, but not limited to, an 11, 13, 14, 16, 17, or 18 gauge.

Body 101 typically includes (or provides access to) a microwave powersource (not shown) for supplying microwave energy to emitter assembly110. Emitter assembly 110 comprises an antenna for emitting themicrowave energy into surrounding tissue when emitter assembly 110 isinserted within a patient's tissue.

Body 101 may also include (or provide access to) a controller (notshown) for controlling the power, frequency, and/or phase of themicrowave energy delivered to emitter assembly 110. In some embodiments,the controller can be configured to automatically adjust the power,frequency, and/or phase of the microwave energy delivered to emitterassembly 110 in order to tune or impedance match the emitter assembly tosurrounding tissue.

The MWA device 100 can be configured to transmit energy having one ormore frequencies or a variable frequency. For example, in someembodiments, the microwave power source is a microwave source configuredto provide microwave energy to emitter assembly 110. Such energy canhave a frequency within the range of about 300 MHz to 30 GHz. In someembodiments, a specific frequency of 915 or 2,450 MHz may be preferred.When microwave energy is delivered to emitter assembly 110, tissuesurrounding emitter assembly 110 can be ablated by heat generated byemitter assembly 110.

Additionally, the microwave power source can be configured to transmitvarious levels of energy to emitter assembly 110. In some embodiments,the microwave power source can transmit up to about 300 W of power toemitter assembly 110. In other embodiments, the microwave power sourcecan transmit between 0 W to 300 W of power to emitter assembly 110,including specifically transmitting up to 40 W, up to 60 W, up to 120 W,up to 180 W, or up to 240 W of power to emitter assembly 110.

In some embodiments, the controller can be configured to ramp up thepower delivered to emitter assembly 110 slowly during the initial phasesof an ablation procedure. Such configurations can incrementally,exponentially, or otherwise ramp up power from zero to a maximum poweroutput over a predetermined time. For instance, the controller can beconfigured to ramp up power delivered to emitter assembly 110 from 0 Wto 60 W over a time period.

During MWA, emitter assembly 110 is inserted through the skin and tissueof a patient, and is then directed toward a target structure, such as atumor, cell(s), or nerve(s). Emitter assembly 110 can be inserted intothe target structure or placed beside the target structure. Microwaveenergy emitted from emitter assembly 110 can then heat the targetstructure, which may be ablated and/or killed. When the target structureis exposed to the transmitted microwave energy for an adequate amount oftime and temperature, the target structure can be ablated. Cancer cells,in particular, can break down and die at elevated temperatures caused byMW ablation procedures. Some MWA procedures create temperatures up to orexceeding 100 to 350 degrees Celsius.

Generally, the shape and size of an ablation pattern produced by emitterassembly 110 roughly corresponds to the shape and intensity of themicrowave transmission patterns of the waves emitted from emitterassembly 110. Thus, a substantially spherical transmission pattern canproduce a roughly spherical ablation pattern. Accordingly, emitterassembly 110 can be configured to produce ablation regions that aresubstantially the same size as the target structure so that theappropriate amount of target tissue is ablated, without ablating healthysurrounding tissues. For example, since many tumors are approximatelyspherical, emitter assembly 110 can be configured to produce a generallyspherical ablation region.

Additionally, emitter assembly 110 can be configured to produce ablationregions that are directional and dose-able (or shapeable) so that theycan be shaped to be the same size as a target structure or so that theycan be directed toward a target structure near emitter assembly 110.Such directionality can be produced, in some instances, by varying thephase between transmitted microwave energy transmitted through multipleconductors of emitter assembly 110.

FIG. 2A illustrates an example configuration of an emitter assembly 200in accordance with one or more embodiments of the invention. Emitterassembly 200 can be used with body 101 as described above, or with anyother type of suitable body that can supply microwave energy to emitterassembly 200.

Emitter assembly 200 comprises a proximal shaft 201, a distal shaft 203,a shunt 202 positioned between and connecting proximal shaft 201 anddistal shaft 203, and a tip 204 positioned at a distal end of distalshaft 203. An exploded view of these four components of emitter assembly200 is shown in FIG. 3.

Emitter assembly 200 also includes a conductor 206 that extends throughemitter assembly 200. Conductor 206 is configured to connect to a sourceof microwave energy (e.g. via body 101) and transmit the microwaveenergy to tip 204 as will be further described below.

Distal shaft 203 includes a distal ring 207 a that extends around distalshaft 203 and is positioned adjacent tip 204. Distal shaft 203 alsoincludes a trace 207 b that extends from distal ring 207 a and wrapsaround distal shaft 203 in a helical pattern. Distal shaft 203 furtherincludes a proximal ring 207 c that extends around distal shaft 203 andis positioned adjacent shunt 202. The connections between conductor 206and distal ring 207 a, trace 207 b, and proximal ring 207 c will befurther described below with reference to FIG. 2B. Although distal ring207 a and proximal ring 207 c are shown as extending completely arounddistal shaft 203, distal ring 207 a and proximal ring 207 c may equallyextend only partially around distal shaft 203. As is further describedbelow, the distal and proximal rings are comprised of a conductivematerial and can serve to interconnect one or more traces with anothercomponent of an emitter assembly.

Although not shown, proximal shaft 201 can contain and circulate acooling fluid (e.g. saline) for cooling emitter assembly 200, and inparticular, for removing heat from shunt 202 and proximal shaft 201.Further, emitter assembly 200 may also include one or more outercoatings 205. In FIG. 2A, outer coating(s) 205 is identified as beingapplied only from shunt 202 and distal shaft 203 (e.g. to cover distalring 207 a, trace 207 b, and proximal ring 207 c. However, in someembodiments, outer coating(s) 205 may also extend overtop tip 204 and/orproximal shaft 201. In other words, outer coating(s) 205 may cover aportion of or the entire outer surface of emitter assembly 200. In someembodiments, outer coating(s) 205 may only be applied overtop distalshaft 203 so as to cover and protect distal ring 207 a, trace 207 b, andproximal ring 207 c as will be further described below.

FIG. 2B provides a cross-sectional view of emitter assembly 200 whileFIGS. 2C, 2D, and 2F each provide a detailed view of a portion of thecross-sectional view of FIG. 2B. FIG. 2E provides a cross-sectional viewof an alternate configuration of shunt 202 in which outer conductor 206c extends only partially into shunt 202.

As shown, shunt 202 is shaped and sized so as to fit within a distal endof proximal shaft 201 and within a proximal end of distal shaft 203.Similarly, tip 204 is shaped and sized so as to fit within a distal endof distal shaft 203. Both shunt 202 and tip 204 are formed of anelectrically and possibly thermally conductive material (e.g. brass,stainless steel, titanium, etc.) that may be suitable for connection viasoldering, brazing or other appropriate means.

Conductor 206 is comprised of a center conductor 206 a, an insulator 206b, and an outer conductor 206 c. Center conductor 206 a extends distallyinto tip 204 and therefore forms an electrical connection with tip 204.Accordingly, microwave energy may be transmitted by center conductor 206a into tip 204. Outer conductor 206 c extends into (if not through asshown in FIG. 2B) shunt 202 and therefore forms an electrical connectionwith shunt 202. In some embodiments, proximal shaft 201 can be made of aconductive material and will therefore form an electrical connectionwith shunt 202 and outer conductor 206 c. Insulator 206 b extends up totip 204 to insulate and isolate center conductor 206 a from the othercomponents of emitter assembly 200. In other embodiments, proximal shaft201 can be made of a non-conductive, low loss dielectric insulator witha low dielectric constant. Suitable insulators include PVC, fiberglass,PEEK, and nylon, among others.

As also shown in FIG. 2B, a void 201 a is formed within proximal shaft201 between the inner wall of proximal shaft 201 and conductor 206. Thecooling fluid mentioned above can circulate within void 201 a to removeheat from the distal end of emitter assembly 200 (e.g. via shunt 202).

As best shown in FIGS. 2D and 2E, proximal ring 207 c forms a coatingnot only on the outer surface of distal shaft 203, but also on thedistal end and the inner surface of distal shaft 203. In someembodiments, including as shown in FIGS. 2D and 2E, proximal ring 207 ccan extend within distal shaft 203 to a depth that is approximately thesame as the depth to which shunt 202 inserts into distal shaft 203. Inthis manner, proximal ring 207 c forms a conductive extension of shunt202 (and therefore outer conductor 206 c) that extends distally alongthe outer surface of distal shaft 203. In typical implementations, outerconductor 206 c functions as a ground, and therefore, in suchimplementations, proximal ring 207 c functions as a ground plane.

As best shown in FIG. 2F, distal ring 207 a can be configured similar toproximal ring 207 c in that it also extends around the distal end ofdistal shaft 203 and onto the inner surface of distal shaft 203. In someembodiments, including as shown in FIG. 2F, distal ring 207 a can extendwithin distal shaft 203 to a depth that is approximately the same as thedepth to which tip 204 inserts into distal shaft 203. In this manner,distal ring 207 a forms a conductive extension of tip 204 (and thereforecenter conductor 206 a).

As is also best shown in FIG. 2F, a distal end of trace 207 b isconnected to distal ring 207 a. Trace 207 b is therefore electricallyconnected with inner conductor 206 a thereby allowing trace 207 b tofunction as an antenna for the microwave energy transmitted via centerconductor 206 a.

As stated above, distal ring 207 a and/or proximal ring 207 c need notextend completely around distal shaft 203. FIG. 2G illustrates anexample where distal ring 207 a extends only partially around distalshaft 203. As shown, distal ring 207 a is not present at the top ofdistal shaft 203. In some embodiments, distal ring 207 a and/or proximalring 207 c may extend around different amounts of the inner and outersurfaces of distal shaft 203. For example, distal ring 207 a may extendcompletely around the inner surface of distal shaft 203 but only extend180 degrees around the exterior surface. Similarly, distal ring 207 amay extend 180 degrees around the inner surface of distal shaft 203while only including a small portion (e.g. similar to the width of trace207 b) that extends around the outer surface. In such cases, it may beaccurate to say that no part of distal ring 207 a extends around theexterior surface, but trace 207 b extends up to and connects with aportion of distal ring 207 a that is formed on an inner surface.

FIGS. 4A-4D illustrate cross-sectional views of distal shaft 203 inisolation. FIG. 4A illustrates distal shaft 203 with distal ring 207 a,trace 207 b, and proximal ring 207 c. FIG. 4B illustrates that outercoating(s) 205 has been applied on distal shaft 203 overtop distal ring207 a, trace 207 b, and proximal ring 207 c. As stated above, outercoating(s) 205, in some embodiments, may only be applied over distalshaft 203 as shown in FIG. 4B while in other embodiments may be appliedover one or more of tip 204, shunt 202, or proximal shaft 201.

In some embodiments, additional inner coatings may be applied to theproximal and/or distal ends of distal shaft 203. For example, as shownin FIG. 4C, a first inner coating 401 may be applied within the proximaland distal ends of distal shaft 203 overtop proximal ring 207 c anddistal ring 207 a. In some embodiments, a second inner coating 402 mayalso be applied overtop of first inner coating 401 as shown in FIG. 4D.First and/or second inner coatings 401/402 can be applied to enhance theconnection and/or increase the conductivity between proximal ring 207 cand shunt 202 and between distal ring 207 a and tip 204. In other words,the connection between proximal ring 207 c and shunt 202 can beincreased by including one or both of inner coatings 401/402 asintermediate layers. Similarly, the connection between distal ring 207 aand tip 204 can be increased by including one or both of inner coatings401/402 as intermediate layers.

In some embodiments of the present invention, distal shaft 203 can beformed of ceramic. For example, distal shaft 203 can be formed fromaluminum oxide, aluminum nitride, zirconia toughened alumina, zirconia,partially stabilized zirconia, silicon carbide, or other ceramicmaterial. Ceramic can be preferred in some embodiments because it is anelectrical insulator that is also strong and tolerant of hightemperatures with low to moderate thermal conductivity. Accordingly, adistal shaft formed of a ceramic can provide high electrical insulationbetween trace 207 b and proximal ring 207 c while also providing thermalconductance to allow heat to be transferred efficiently from tip 204 toshunt 202 where it can be dissipated via the cooling fluid withinproximal shaft 201. This cooling of emitter assembly 200 can assist inenabling emitter assembly 200 to obtain spherical ablations.

In embodiments where distal shaft 203 is formed of ceramic, distal ring207 a, trace 207 b, and proximal ring 207 c can be formed of a metalconductor such as silver, copper, gold, aluminum, nickel, molybdenum(“moly”) manganese, brass, or other conductor. In particular, theceramic distal shaft can be metallized to form distal ring 207 a, trace207 b, and proximal ring 207 c with tight bonding to distal shaft 203.This tight bonding can be formed by heating the metal to hightemperatures while on the ceramic so that the metal adheres to theceramic. Metallizing ceramic refers to the process of applying one ormore layers of metal on the surface of the ceramic and then heating theceramic to cause the metal to bond with the ceramic. Various techniquesexist for metallizing ceramic that would be suitable for metallizing acomponent of an emitter assembly. For example, a thick film inkcontaining a moly manganese refractory formula or another metal can beapplied through a screen, roll printing, hand painting, air brushspraying, immersion, centrifugal coating, needle painting, etc. to aceramic component and fired at temperatures sufficient to cause bondingof the metal to the ceramic.

Outer coating(s) 205 can be employed to cover distal ring 207 a, trace207 b, and proximal ring 207 c for various reasons including to isolatethem from a patient's tissue, to protect them from decomposition (e.g.via oxidation), and to provide a smooth surface. In some embodiments,outer coating(s) 205 can be comprised of glass or ceramic which may bepreferred due to its high dielectric value which helps microwavesemitted from trace 207 b transition into surrounding tissue.

In some embodiments, a material that provides a non-stick surface may bepreferred and multiple coatings may be used for outer coating(s) 205.For example, outer coating(s) 205 can be formed of glass orPolytetrafluoroethylene (PTFE) to prevent ablated tissue from stickingto the outer surface of emitter assembly 200 (e.g. to the outer surfaceof tip 204, distal shaft 203, shunt 202, and/or proximal shaft 201). Insome embodiments, a glass outer coating(s) 205 can be employed with anadditional PTFE coating overtop the glass. In this way, the benefits ofa glass coating can be obtained while also having a non-stick PTFE ordiamond-like carbon surface.

In some embodiments, tip 204 may also be formed of a ceramic. In suchcases, a conductive coating (e.g. a copper, silver, nickel, gold or molymanganese coating) can be applied to the inner surfaces of tip 204 toform an electrical connection between distal ring 207 a and centerconductor 206 a. Forming tip 204 of ceramic can be preferred inembodiments where it is desirable that the visibility of tip 204 viax-ray be minimized. In other embodiments, tip 204 can be formed ofbrass, titanium, or low thermo-expansion metals.

In some embodiments of the invention, insulator 206 b may be formed ofPTFE. In other embodiments, however, insulator 206 b may be formed of aceramic such as an aluminum oxide based ceramic to enhance thedissipation of heat from within center conductor 206 a. A ceramicinsulator 206 b would also be able to withstand higher temperatures thanTeflon. For example, Teflon can melt when center conductor 206 a heatsit to above 300° C. which can occur during high power transmission. Byusing a ceramic insulator 206 b, emitter assembly 200 could be operatedat higher wattages without the risk of melting insulator 206 b. Thisability to operate at higher temperatures and wattages would enableemitter assembly 200 to be used to perform larger diameter ablations.

In some embodiments, first inner coating 401 can be comprised of molymanganese while second inner coating 402 can be comprised of nickel. Insome embodiments, a third inner coating may also be employed and may becomprised of gold, copper, silver, or another metal. Employing secondinner coating 402 (and in some cases, a third inner coating) can bepreferred because it enables tip 204 and shunt 202 to be secured todistal shaft 203 by soldering or brazing. In some embodiments, proximalshaft 201 can be formed of stainless steel. In some embodiments, outerconductor 206 c can be formed of solder filler although any conductivematerial can be used. In some embodiments, a dielectric material may bedisposed within the void (not labeled) between the inner surface ofdistal shaft 203 and insulator 206 b. For example, a PTFE, polyimide(e.g. Kapton®), silicone, a high temperature resistant polymer, or aceramic material could be used. In some embodiments, insulator 206 b canbe configured with a sufficient diameter so that there is little or novoid.

FIGS. 5A and 5B illustrate various dimensions of distal shaft 203including of distal ring 207 a, trace 207 b, proximal ring 207 c, andouter coating(s) 205. The specific dimensions may vary based on theintended use of emitter assembly 200. For example, the dimensions mayvary based on the frequency (or wavelength) of the microwave energyemployed as will be apparent to one of skill in the art.

The following dimensions are exemplary dimensions for an embodiment ofemitter assembly 200 that is tuned for use at 915 MHz. These exemplarydimensions should not be construed as limiting the invention to anemitter assembly tuned to any particular frequency. Other dimensionscould be employed and can be based on various factors including thefrequency or frequencies at which the particular emitter assembly willbe operated, the power at which the emitter assembly will be operated,the intended ablation pattern, etc.

With reference to FIG. 5A, the diameter of distal shaft 203 (dimensiong) in this embodiment is 0.083 inches. However, a suitable diameter mayalso be within a range from 0.02 to 0.25 inches. The width of distalring 207 a and trace 207 b and the spacing between portions of trace 207b (dimensions d, e, and f) is approximately 0.04 inches. However, asuitable width may also be within a range from 0.001 to 0.2 inches. Thewidth of proximal ring 207 c (dimension a) as well as the spacingbetween proximal ring 207 c and trace 207 b (dimension b) can be thesame and in this embodiment is 0.1 inches. However, a suitable width andspacing may also be within a range from 0.001 to approximately 0.5inches. The length of distal shaft 203 along which trace 207 b extends(dimension c) is between 0.01 and 4.0 inches. The total length of trace207 b (i.e. the length passing around distal shaft 203) is between 0.1and 9.0 inches. The total number of revolutions of trace 207 b isapproximately between 0.5 and 50.

With reference to FIG. 5B, the length of distal shaft 203 (dimension j)is approximately 0.45 inches. However, a suitable length may also bewithin a range from 0.02 to 4.0 inches. The internal diameter of distalshaft 203 (dimension i) is approximately 0.043 inches. However, asuitable internal diameter may also be within a range from 0.005 to 0.25inches. The thickness of distal ring 207 a, trace 207 b, and proximalring 207 c (dimension k) is approximately 0.001 inches. However, asuitable thickness may also be within a range from 0.0001 to 0.004inches. The depth of outer coating(s) 205 (dimension l) is approximatelybetween 0.0001 and 0.003 inches. The width of proximal ring 207 c anddistal ring 207 a within distal shaft 203 (dimensions m and nrespectively) is approximately 0.04 inches. However, a suitable widthmay also be within a range from 0.005 to 0.25 inches. Although notshown, the thickness of first inner coating 401 can be between 0.0001and 0.002 inches while the thickness of second inner coating 402 can bebetween 0.00005 and 0.001 inches when such coatings are employed. Also,conductor 206 can be configured with an outer diameter of approximately0.047 inches. However, suitable outer diameters may also be within arange from 0.002 to 0.125 inches.

Variations in the above dimensions can also be employed even whenconfiguring emitter assembly 200 for operation at 915 MHz. For example,optimal performance at 915 MHz may be obtained when dimensions e and fare set to different values (e.g. between 0.001 and 0.2 inches) or whenthe dimensions remain equal or substantially similar. In someembodiments, a different pattern for trace 207 b can be employed otherthan the helical pattern depicted in the figures as long as dimensions eand f remain consistent with respect to one another. In otherembodiment, dimensions e and f may not remain consistent. Suitablepatterns include a back-and-forth spiraling pattern (as opposed to thedepicted wrap-around helical pattern) or a stepped-up helical pattern(as opposed to the depicted gradually increasing or decreasing helicalpattern).

In some embodiments, trace 207 b may have a variable pattern. Forexample, the pitch of a helical or other pattern may vary. Varying thepitch can change the field intensity of the microwaves emitted from thetrace. A smaller pitch will cause the windings of a helical trace to bespaced more closely and will therefore increase the field intensityalong the portion of the emitter assembly with the smaller pitchedtrace. Traces that are more closely spaced will also create a greaterdensity of heat. Accordingly, the pitch of a trace may be reduced nearerthe proximal end of distal shaft 203 so that the heat density isgreatest nearer proximal shaft 201. This can facilitate the transfer ofheat to proximal shaft 201. In some embodiments, proximal and distalportions of trace 207 b may have a smaller pitch than a middle portionof the trace such that the trace is more closely spaced in the proximaland distal portions than in the middle portion. Varying the pitch inthis manner may create a spherical radiation pattern or potentiallyanother desired non-spherical radiation pattern.

The width of trace 207 b may also be varied. A thicker trace will allowmore current flow. Accordingly, in some embodiments, a distal portion ofthe trace 207 b may be thicker than a proximal portion to account forhigher currents that pass through the distal portion.

FIG. 6 illustrates a variation of distal shaft 203 shown in FIG. 5A. Asshown in FIG. 6, the proximal end 601 of trace 207 b can be rounded.However, the proximal end 601 of trace 207 b may also be square asdepicted in the other figures, or may be another suitable shape.

FIG. 7 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 7, trace 207 b can include an extension 701 thatconnects trace 207 b to proximal ring 207 c. In a typical implementationwhere trace 207 b receives microwave energy and proximal ring 207 c isconnected to ground, extension 701 can function to close the circuit.Using extension 701 in this manner can enable an emitter assembly (e.g.emitter assembly 200) to produce more heat over a time period andtransmit higher powers. For example, by closing the circuit, extension701 can make trace 207 b (which functions as an antenna) lesssusceptible to changes in the surrounding tissue (e.g. changes inconductance, dielectric constant, etc.) that occur during an ablationprocedure. Although extension 701 is shown as extending from theproximal most portion of trace 207 b, it may also be positioned toextend from other locations along trace 207 b. Extension 701 can alsohave other shapes in addition to the straight line shape shown in FIG.7. In short, any extension that connects trace 207 b and proximal ring207 c can be employed.

FIG. 8 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 8, trace 207 b can have a varied pitch with portion801 of trace 207 b having a smaller pitch than the more distal portions.

FIG. 9 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 9, trace 207 b can have a varied width with adistal portion of trace 207 b being thicker than a proximal portion.

FIG. 10 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 10, distal shaft 203 does not include a proximalring.

FIG. 11 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 11, proximal ring 207 c comprises a distallyextending trace 207 d. In some embodiments, such as shown in FIG. 11, agap may exist between trace 207 b and trace 207 d. Alternatively, trace207 d may extend up to and even connect with trace 207 b. Trace 207 dcan have any suitable pattern including any of the variations asdescribed above for trace 207 b.

FIG. 12 illustrates another variation of distal shaft 203 shown in FIG.5A. As shown in FIG. 12, distal shaft 203 does not include a distalring, but includes a proximal ring 207 c and a distally extending trace207 d. In such embodiments, trace 207 d could be electrically connectedto inner conductor 206 a (e.g. via proximal ring 207 c) to therebyfunction as an antenna.

FIG. 13 illustrates another variation of the distal shaft shown in FIG.5A. As shown in FIG. 13, distal shaft 203 includes a distal ring 207 athat extends only partially around distal shaft 203. Trace 207 bconnects with and extends from distal ring 207 a. Distal ring 207 a mayextend around a similar portion or a different portion of the innersurface of distal shaft 203 or may extend completely around the innersurface.

FIG. 14 illustrates another example emitter assembly 1400 that isconfigured in accordance with the above description. Emitter assembly1400 includes a trace that extends around the distal shaft 3.5 times ina helical pattern. An outer dielectric coating (e.g. glass) covers theentire emitter assembly (i.e. the tip, distal shaft, shunt, and proximalshaft). A shunt extends into both the proximal shaft and the distalshaft and functions to form an electrical connection between the outerconductor and the proximal ring, and to form a thermal connectionbetween the tip and the cooling fluid contained within the proximalshaft.

The present invention encompasses additional variations to the designdescribed above. In some embodiments, an emitter assembly may notinclude shunt 202. For example, proximal shaft 201 and distal shaft 203may be configured to directly couple together such as by brazing a jointbetween the two components or configuring an end of one component toinsert within the end of the other component. In such cases, if aproximal ring 207 c is included, distal shaft 203 can be configured toform an electrical connection between proximal ring 207 c and outerconductor 206 c (assuming distal ring 207 a and trace 207 b are used toform an antenna) or between proximal ring 207 c and inner conductor 206a (assuming proximal ring 207 c will function as the antenna).

In some embodiments, distal shaft 203 can be configured to form tip 204rather than have a separate component for tip 204. In such cases, distalshaft 203 and tip 204 can comprise a single component formed of ceramic.In such embodiments, a distal ring 207 a and trace 207 b may not beincluded. Instead, proximal ring 207 c may comprise a distally extendingtrace (e.g., similar to trace 207 d) which is connected to innerconductor 206 a. Alternatively, a distal ring 207 a and trace 207 bcould be formed with distal shaft 203 including an opening or otherelectrically conductive channel for connecting inner conductor 206 awith distal ring 207 a.

In some embodiment, tip 204 can be formed of a non-conductive material.In such embodiments, distal ring 207 a can extend onto an inner surfaceof distal shaft 203 to which inner conductor 206 a can connect.Similarly, shunt 202 could be formed of a non-conductive material withproximal ring 207 c extending onto an inner surface of distal shaft 203for connecting outer conductor 206 c (or, in some cases, inner conductor206 a) to proximal ring 207 c.

In some embodiments, tip 204 can be comprised of two components. Aninner component may be formed of a conductive material (e.g., a metal)which interconnects inner conductor 206 a with distal ring 207 a. Anouter component may function as an end cap that is placed overtop theinner component. The outer component, in some embodiments, may becomprised of ceramic.

FIGS. 15A-15C illustrate different views of a tip 1500 that can be usedin place of distal shaft 203 and tip 204. Tip 1500 comprises anon-conductive material such as ceramic. A proximal end of tip 1500 canbe configured to insert into proximal shaft 201 when shunt 202 is notemployed or to connect to proximal shaft 201 via shunt 202. A distallyextending trace 1501 is formed on the outer surface of tip 1500. Trace1501 includes an extension 1501 a that extends onto an inner surface oftip 1500. When tip 1500 is connected to proximal shaft 201, whetherdirectly or via shunt 202, inner conductor 206 a can be connected toextension 1501 a thereby supplying microwave energy to trace 1501. Tip1500 can also include a metalized portion 1502 or forming an electricalconnection with outer conductor 206 c.

In other embodiments, tip 1500 may be used in conjunction with distalshaft 203. In such embodiments, portion 1502 can be electricallyconnected via outer conductor 206 c to distal ring 207 a therebyallowing trace 207 b to form a ground plane. In some embodiments, aninsulative coating (not shown) can be applied on tip 1500 prior toforming trace 1501. One or more outer coatings (e.g., similar to outercoating(s) 205) may also be applied after trace 1501 is formed.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

We claim:
 1. An emitter assembly for performing an ablation comprising:a proximal shaft; a distal shaft having an exterior surface; a tip thatextends from a distal end of the distal shaft; an inner conductor thatextends through the proximal shaft; an outer conductor; and a conductivetrace metalized to the exterior surface of the distal shaft.
 2. Theemitter assembly of claim 1, wherein the distal shaft is comprisedprimarily of ceramic.
 3. The emitter assembly of claim 2, wherein theceramic comprises one of or both alumina based ceramics and zirconiabased ceramics.
 4. The emitter assembly of claim 1, wherein the tip is aseparate component from the distal shaft.
 5. The emitter assembly ofclaim 1, wherein the conductive trace spirals around the exteriorsurface.
 6. The emitter assembly of claim 1, wherein a conductive distalring is formed on one or both of an interior surface or an exteriorsurface of the distal shaft.
 7. The emitter assembly of claim 6, whereinthe tip forms an electrical connection between the inner conductor andthe distal ring.
 8. The emitter assembly of claim 6, wherein theconductive trace is electrically connected to the distal ring.
 9. Theemitter assembly of claim 1, wherein a conductive proximal ring isformed on one or both of an interior or an exterior surface of thedistal shaft.
 10. The emitter assembly of claim 9, wherein theconductive trace is electrically connected to the proximal ring.
 11. Theemitter assembly of claim 1, wherein the conductive trace extends in aproximal direction, and wherein a second conductive trace is formed onthe exterior surface of the distal shaft that extends in a distaldirection.
 12. The emitter assembly of claim 1, further comprising: ashunt that connects the proximal shaft to the distal shaft.
 13. Theemitter assembly of claim 12, wherein the shunt forms an electricalconnection with the outer conductor.
 14. The emitter assembly of claim13, wherein a conductive proximal ring is formed on one or both of aninterior or an exterior surface of the distal shaft, the proximal ringbeing electrically connected to the shunt.
 15. The emitter assembly ofclaim 12, wherein the distal shaft includes one or both of a conductiveproximal ring and a conductive distal ring, and wherein the conductivetrace extends from one or both of the proximal ring and distal ring. 16.The emitter assembly of claim 1, wherein the conductive trace extends inone of a proximal direction or a distal direction.
 17. The emitterassembly of claim 1, further comprising: an insulator positioned betweenthe inner and outer conductors, the insulator comprising PTFE orceramic.
 18. The emitter assembly of claim 1, further comprising: anouter coating comprising one or more layers, the outer coating coveringat least a portion of an exterior surface of the distal shaft.
 19. Theemitter assembly of claim 18, wherein the outer coating covers one ormore of the tip, a shunt that connects the proximal shaft to the distalshaft, or the proximal shaft.
 20. The emitter assembly of claim 18,wherein the outer coating comprises at least one of glass, PTFE, ordiamond-like carbon.
 21. The emitter assembly of claim 1, furthercomprising: one or more inner coatings applied on an inner surface ofthe distal shaft.
 22. The emitter assembly of claim 21, wherein one orboth of a conductive proximal ring and a conductive distal ring areformed on an exterior surface of the distal shaft, and wherein the oneor more inner coatings are applied overtop a portion of one or both ofthe proximal ring and distal ring that extends along the inner surface.23. The emitter assembly of claim 1, wherein the tip is comprised of aninner and an outer component.